The present invention generally relates to a sponge having improved rubber elasticity and its manufacturing method and more particularly to a sponge with an improved gentle feel and its manufacturing method.
Conventionally, a sponge having rubber elasticity is typically made from a material obtained by foam molding using polyurethane or other polymer elastomers, rubber or other materials. Such sponges have been used as washing implements, cosmetic implements, coating tools, wiping tools, cushion material, transporting parts, packing parts and in a variety of other fields. In the case of washing implements, cosmetic implements, coating tools, wiping tools, and cushion material, a sponge with a soft, gentle feel has been required. This requirement can be met in several ways during manufacture of the sponge. For example, a soft gentle texture can be achieved by decreasing the surface roughness with fine gas bubbles with a gas bubble diameter of 200 xcexcm or less. The sponge can be made puffy with an apparent specific gravity of 0.10 g/cm3 or less. Finally, the apparent rubber hardness can be suppressed to a low level or a soft resin can be used.
However, although decreasing the gas bubble diameter results in reducing the roughness and a smooth feel is achieved, a dry texture is produced at the same time. Furthermore, while decreasing the apparent specific gravity results in a puffy sponge, a gentle feel is not produced. On the contrary, a sticky texture is produced in an undesirable manner. Moreover, in decreasing the apparent specific gravity, there are other problems in that the mechanical strength is decreased, foam molding is difficult, shrinkage deformation occurs during molding, and internal cracks are formed. Furthermore, making the gas bubbles small and decreasing the apparent specific gravity are contradictory with each other. In particular, it is very difficult to achieve these goals at the same time. Alternatively, if a soft resin is used, although the sponge is made soft, a tacky feel due to poor rubber elasticity is produced. In addition, such soft resins are inherently characterized with a low mechanical strength. Thus, a gentle feel cannot be achieved by any of these methods.
Accordingly, it would be desirable to provide a sponge having an improved gentle texture that is not made by conventional prior art techniques.
The present invention is a sponge with an improved gentle feel. As a result of zealous research investigations, the present inventors have discovered that a gentle feel can be obtained by containing a lipid, such as an oil, a fat, or a combination thereof in the sponge. In other words, the sponge of the present invention is a material characterized by the fact that an oil, a fat, or a combination thereof is contained in a sponge having rubber elasticity.
In a preferred embodiment, the sponge of the present invention generally includes an elastic material having a lipid, such as an oil, a fat, or a combination thereof, integrally formed therewith. Preferably, the elastic material includes an amount from between 0.5 to 20 parts by weight of the lipid, and the lipid is selected from the group consisting of esters of fatty acids, alkanes, squalane and derivatives thereof, squalene, bisabolol, animal hair oils and fats, wax, lanolin and combinations thereof. The elastic material further preferably includes a nonionic surfactant integrally formed therewith in an amount from between 0.5 to 20 parts by weight of the nonionic surfactant.
In an alternate embodiment, the sponge of the present invention generally includes an elastic material having a lipid, such as an oil a fat, or a combination thereof, that is substantially inseparable from the elastic material. Preferably, the elastic material includes an amount from between 0.5 to 20 parts by weight of the lipid, and the lipid is selected from the group consisting of esters of fatty acids, alkanes, squalane and derivatives thereof, squalene, bisabolol, animal hair oils and fats, wax, lanolin and combinations thereof. The elastic material further preferably includes a nonionic surfactant integrally formed therewith in an amount from between 0.5 to 20 parts by weight of the nonionic surfactant.
In a preferred method for forming the sponge of the present invention, an elastic material is mixed with a lipid, such as an oil, a fat or a combination thereof, and the elastic material and lipid mixture is foam molded to form the sponge. Preferably, an amount from between 0.5 to 20 parts by weight of lipid is mixed with the elastic material and the lipid is selected from the group consisting of esters of fatty acids, alkanes, squalane and derivatives thereof, squalene, bisabolol, animal hair oils and fats, wax, lanolin and combinations thereof. The elastic material and lipid is further preferably mixed with a nonionic surfactant in an amount from between 0.5 to 20 parts by weight of the nonionic surfactant.
In an alternate method for forming the sponge of the present invention, a sponge is first foam molded from an elastic material. The sponge is then impregnated with a water-dispersed lipid and allowed to dry for a predetermined amount of time so that the lipid is substantially inseparable from the elastic material. The lipid is preferably selected from the group consisting of esters of fatty acids, alkanes, squalane and derivatives thereof, squalene, bisabolol, animal hair oils and fats, wax, lanolin and combinations thereof.
A preferred embodiment of an elastic sponge and its method of manufacture as well as other embodiments, features and advantages of this invention will be apparent from the following detailed description, which is to be read in conjunction with the accompanying examples.
The improved texture of the sponge of the present invention is produced by containing a lipid, i.e., an oil, a fat, or a combination thereof, in the sponge. Preferably, the lipids used in the present invention include naturally and artificially obtained fatty acid esters, lanolin, oils and fats extracted from animal hair, squalane and its derivatives, squalene (oils and fats extracted from deep sea sharks and related artificial products), bisabolol, wax, etc. and mixtures thereof. The amount of their usage is 0.5-20 parts by weight, preferably 1.0-10 parts by weight, with respect to 100 parts by weight of the raw material resin. If more is used, a gentle feel cannot be achieved, but instead a tacky feel will be produced in an undesirable manner. Furthermore, if more than 20 parts by weight oil or fat is used, collapsing of bubbles will occur during foam molding and a uniform sponge cannot be obtained.
It is further preferable to use oils and fats in combination with a polyoxyethylene alkyl ether or another nonionic surfactant. By combining a nonionic surfactant with the lipid, collapsing of bubbles will not easily occur during foam molding. It is preferable that the nonionic surfactant be used at 0.5-20 parts by weight with respect to 100 parts by weight of the raw material resin.
The base material for the sponge is preferably one having superior rubber elasticity obtained by open cell or closed cell foam molding of polyurethane, rubber or other polymer elastomers, including polyethylene type elastomers, vinyl type elastomers, etc. Of the above mentioned elastomers, polyurethane is preferred. The elastomer can be provided in pure resin form or can be in emulsion. Furthermore, a polyol and an isocyanate as resin raw materials can also be used like polyurethane. Suitable rubbers for the sponge of the present invention include NR, DPNR, NBR, IR, BR, SBR, CR, EPDM, silicone rubber, acrylic rubber, or mixtures thereof. Furthermore, the rubber used can be a latex or can be in resin form.
The sponge of the present invention is manufactured by foam molding of a mixture of a raw material resin and at least one lipid. A variety of other additives can also be introduced into the mixture as described below. Any conventional method for foam molding can be used. For example, in the method of foaming by the generation of a gas, the gas is generated by a method in which a blowing agent is mixed in a raw material resin followed by heating, and then foam molding is carried out. Alternatively, foam molding can be carried out by blending a water-soluble salt in a raw material resin, molding, and forming pores by dissolution and extraction of the salt in water. Another alternative method is by dissolving a raw material resin in a water-soluble solvent, and forming pores by extraction of the solvent by introducing this resin solution into water. Furthermore, it is possible for a raw material resin to be converted into an emulsion or latex, and for air or the like to be stirred or mixed in to cause foaming, and molding to be carried out.
Where polyurethane resin is used as the base material, it is preferred that the lipid, an additive and a blowing agent be mixed with a polyol as a resin raw material, and for this to be reacted with an isocyanate to cause the generation of a gas at the same time as the formation of the resin, followed by foam molding.
In mixing the lipid with the elastomer resin, it is preferred to use a method in which the lipid is dissolved or dispersed in the resin. Furthermore, it is also possible for a water-dispersed lipid to be prepared first, and to be mixed into a raw material emulsion or latex.
It is also possible for the sponge of the present invention to be manufactured by a method in which the oils and fats mentioned previously are adhered onto a sponge prepared beforehand. For example, the lipid can be converted into a water-dispersed material that is introduced into the sponge and allowed to dry.
The lipids introduced into the sponge bleed on the surface of the resin that forms the frame or skeleton of the sponge and a thin film is thereby formed. This results in a sponge having an improved gentle feel and a frictional coefficient of the sponge on the magnitude of 0.2 to 0.5.
It is desirable that the average cell size, i.e., gas bubble diameter, for the sponge of the present invention be 200 xcexcm or less, and more preferably 150 xcexcm or less. By decreasing the average gas bubble diameter, the gentle feel is emphasized. This is presumably due to the fact that the resin portion forming the gas bubble frame becomes more detailed, i.e., more cells appear per unit area, and there is an amplified effect because of coating of each of these cells by the lipid. In this case, it is possible that the amount of the lipid used can be decreased to 0.5 part by weight with respect to 100 parts by weight of the raw material resin. The gas bubble diameter can be reduced, for example, by atomizing the blowing agent, by increasing the rotational speed of the mixer during foaming and/or by increasing the apparent specific gravity of the resin among other ways.